In semiconductor technology, GaN is used to form various integrated circuit devices, such as high power field-effect transistors, metal insulator semiconductor field effect transistors (MISFETs), high frequency transistors, high power Schottky rectifiers, and high electron mobility transistors (HEMTs). These devices can be formed by growing epitaxial layers, which can be grown on silicon, silicon carbide, sapphire, gallium nitride, or other substrates. Often, devices are formed using a heteroepitaxial junction of AlGaN and GaN. This structure is known to form a high electron mobility two-dimensional electron gas (2DEG) at the junction. Sometimes additional layers are added to improve or modify the charge density and mobility of electrons in the 2DEG. In a conventional GaN transistor, the device is normally in a conducting, or “on” state. In some applications it may be desirable to have other normal states of GaN devices that may provide improved efficiency, performance or other features.